GRASS allows all geometry types (point, line and polygon) in one vector map,
but QGIS requires a layer to have a specific type.

OpenStreetMap

QGIS OSM support is in menu (Vector > OpenStreetMap),
which can download and import OSM files by geometry type
and with selected tags via a SpatiaLite database connection.
OSM's 64-bit identifier is supported in QGIS.